Hi Leonard, [FYI, it's a private test report for your RFC patch.] [auto build test WARNING on next-20210420] [also build test WARNING on v5.12-rc8] [cannot apply to linus/master v5.12-rc8 v5.12-rc7 v5.12-rc6] [If your patch is applied to the wrong git tree, kindly drop us a note. And when submitting patch, we suggest to use '--base' as documented in https://git-scm.com/docs/git-format-patch] url: https://github.com/0day-ci/linux/commits/Leonard-Crestez/tcp-Delay-sendin... base: 593ef1658ecf61d3619885bdbbcfffa3d1417891 config: x86_64-randconfig-a015-20210421 (attached as .config) compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project d87b9b81ccb95217181ce75515c6c68bbb408ca4) reproduce (this is a W=1 build): wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross chmod +x ~/bin/make.cross # install x86_64 cross compiling tool for clang build # apt-get install binutils-x86-64-linux-gnu # https://github.com/0day-ci/linux/commit/0b2ec1d5d492384a89a499c7227c7f6a2... git remote add linux-review https://github.com/0day-ci/linux git fetch --no-tags linux-review Leonard-Crestez/tcp-Delay-sending-non-probes-for-RFC4821-mtu-probing/20210421-182309 git checkout 0b2ec1d5d492384a89a499c7227c7f6a21f283d0 # save the attached .config to linux build tree COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 ARCH=x86_64 If you fix the issue, kindly add following tag as appropriate Reported-by: kernel test robot <lkp(a)intel.com&gt; All warnings (new ones prefixed by >>): net/ipv4/tcp_output.c:188:3: warning: result of comparison of constant -1 with expression of type 'u8' (aka 'unsigned char') is always false [-Wtautological-constant-out-of-range-compare] NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPACKCOMPRESSED, ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ include/net/ip.h:290:41: note: expanded from macro 'NET_ADD_STATS' #define NET_ADD_STATS(net, field, adnd) SNMP_ADD_STATS((net)->mib.net_statistics, field, adnd) ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ include/net/snmp.h:143:4: note: expanded from macro 'SNMP_ADD_STATS' this_cpu_add(mib->mibs[field], addend) ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ include/linux/percpu-defs.h:509:33: note: expanded from macro 'this_cpu_add' #define this_cpu_add(pcp, val) __pcpu_size_call(this_cpu_add_, pcp, val) ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ note: (skipping 1 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all) <scratch space>:218:1: note: expanded from here this_cpu_add_8 ^ arch/x86/include/asm/percpu.h:326:35: note: expanded from macro 'this_cpu_add_8' #define this_cpu_add_8(pcp, val) percpu_add_op(8, volatile, (pcp), val) ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ arch/x86/include/asm/percpu.h:127:31: note: expanded from macro 'percpu_add_op' ((val) == 1 || (val) == -1)) ? \ ~~~~~ ^ ~~ void tcp_mtu_probe_wait_stop(struct sock *sk) ^ net/ipv4/tcp_output.c:1759:1: note: declare 'static' if the function is not intended to be used outside of this translation unit void tcp_mtu_probe_wait_stop(struct sock *sk) ^ static 2 warnings generated. vim +/tcp_mtu_probe_wait_stop +1759 net/ipv4/tcp_output.c 1758 1760 { 1761 struct inet_connection_sock *icsk = inet_csk(sk); 1762 1763 if (icsk->icsk_mtup.wait_data) { 1764 icsk->icsk_mtup.wait_data = false; 1765 sk_stop_timer(sk, &icsk->icsk_mtup.wait_data_timer); 1766 } 1767 } 1768 --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org